[clang-format] Don't wrap struct return types as structs

When using BraceWrapping.AfterClass or BraceWrapping.AfterStruct, the
token annotator relies on the first token of the line to determine if
we're dealing with a struct or class, however, this check is faulty if
it's actually a function with an elaborated struct/class return type, as
is common in C.

This patch skips the check if the brace is already annotated as
FunctionLBrace, in which case we already know it's a function and should
be treated as such.

Fixes #58527

Reviewed By: HazardyKnusperkeks, owenpan

Differential Revision: https://reviews.llvm.org/D146281

Author: rymiel

clang/lib/Format/TokenAnnotator.cpp

@@ -4916,8 +4916,13 @@ bool TokenAnnotator::mustBreakBefore(const AnnotatedLine &Line,
       return true;
     }
 
-    return (Line.startsWith(tok::kw_class) && Style.BraceWrapping.AfterClass) ||
-           (Line.startsWith(tok::kw_struct) && Style.BraceWrapping.AfterStruct);
+    // Don't attempt to interpret struct return types as structs.
+    if (Right.isNot(TT_FunctionLBrace)) {
+      return (Line.startsWith(tok::kw_class) &&
+              Style.BraceWrapping.AfterClass) ||
+             (Line.startsWith(tok::kw_struct) &&
+              Style.BraceWrapping.AfterStruct);
+    }
   }
 
   if (Left.is(TT_ObjCBlockLBrace) &&

clang/unittests/Format/FormatTest.cpp

@@ -3205,17 +3205,50 @@ TEST_F(FormatTest, MultiLineControlStatements) {
             format("try{foo();}catch(...){baz();}", Style));
 
   Style.BraceWrapping.AfterFunction = true;
+  Style.BraceWrapping.AfterStruct = false;
   Style.BraceWrapping.AfterControlStatement = FormatStyle::BWACS_MultiLine;
   Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_All;
   Style.ColumnLimit = 80;
   verifyFormat("void shortfunction() { bar(); }", Style);
+  verifyFormat("struct T shortfunction() { return bar(); }", Style);
+  verifyFormat("struct T {};", Style);
 
   Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_None;
   verifyFormat("void shortfunction()\n"
                "{\n"
                "  bar();\n"
                "}",
                Style);
+  verifyFormat("struct T shortfunction()\n"
+               "{\n"
+               "  return bar();\n"
+               "}",
+               Style);
+  verifyFormat("struct T {};", Style);
+
+  Style.BraceWrapping.AfterFunction = false;
+  Style.BraceWrapping.AfterStruct = true;
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_All;
+  verifyFormat("void shortfunction() { bar(); }", Style);
+  verifyFormat("struct T shortfunction() { return bar(); }", Style);
+  verifyFormat("struct T\n"
+               "{\n"
+               "};",
+               Style);
+
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_None;
+  verifyFormat("void shortfunction() {\n"
+               "  bar();\n"
+               "}",
+               Style);
+  verifyFormat("struct T shortfunction() {\n"
+               "  return bar();\n"
+               "}",
+               Style);
+  verifyFormat("struct T\n"
+               "{\n"
+               "};",
+               Style);
 }
 
 TEST_F(FormatTest, BeforeWhile) {